Page 17 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 5

Nutrient elements are supplied gradually to plants. Initially, plant roots
absorb nutrients from the most readily available forms in soils, i.e. soil soluble
nutrients in soil water (free ions and complex ions), classified as Intensity Factor.
As the concentration of soil soluble forms is lowered due to absorption by plant
roots, the Capacity Factor supplies the nutrient elements. The soil labile fractions
are the first soil Capacity Factor to supply the nutrient elements to satisfy the
equilibrium shifting by releasing nutrient elements into soil water. The most
readily available labile fractions are the exchangeable elements or the surface
elements because these forms are attached onto the soil solids with relatively low
energies. As the concentrations of nutrients in the soil labile fractions decrease,
the more stabile forms of elements in soil mineral structure or organic matters will
be detached and released into soil water and can be absorbed by plant roots. The
release of the structural elements in soil minerals will occur through weathering,
while that of the soil organic mattters occur through decomposition or decay
processes. In the long term, these processes are of great importance because the
soil minerals and the organic matters are composed of the most part of elements in
the soil system. The soil capacity in supplying nutrient elements can be judged
from the amounts of nutrient elements in these materials.

READILY AVAILABLE •FREE IONS MODERATELY AVAILABLE •PRECIPITATES SLOWLY AVAILABLE •PRIMARY
MINERALS
•COMPLEX IONS
•ORGANIC

MATTERS
•EXCHANGEABLE
NUTRIENTS
•PARTS OF
PRIMARY
MINERALS

Fig. 1.2. Categories and availabilities of nutrient sources in soils (Salam, 2012).

1.2 Supplying Nutrient Elements from Mineral Sources

Soil minerals are the main sources of available nutrient elements in mineral
soils. These compounds supply most of the nutrients needed by plants.

Abdul Kadir Salam - 2014